1. Field of the Invention
The present invention relates to loudspeakers that utilize a diaphragm having high joining strength to a voice coil bobbin, and more specifically to a loudspeaker in which a dome diaphragm made of a base material impregnated in a thermosetting resin is exposed to a front side, and a cone diaphragm and a voice coil bobbin are both coupled to the dome diaphragm.
2. Description of the Related Art
In many cases, loudspeakers employ an assembly structure in which an end of an inner circumference of a loudspeaker diaphragm (especially, cone-shaped diaphragm) is joined with adhesive to a side wall of a cylindrical voice coil bobbin. In some conventional loudspeakers, various efforts are made to the assembly structure in order to reduce the number of assembling steps. Further, as adhesive strength between a voice coil bobbin and a loudspeaker diaphragm in a loudspeaker affects characteristics of sound to be played, various efforts have been made in order to improve the adhesive strength.
As one of such efforts, the applicant of the present invention has provided a loudspeaker diaphragm that can improve the adhesive strength between a voice coil bobbin and a loudspeaker diaphragm (Japanese Patent No. 3846497). As shown in FIG. 2 of Japanese Patent No. 3846497, a loudspeaker diaphragm 5 includes a first diaphragm section 5, a second diaphragm section 6 integrally formed with the first diaphragm section 5, and an attachment 7 that is provided protrudingly toward a back side of a joint portion between the first diaphragm section 5 and the second diaphragm section 6 and to which one end of a voice coil bobbin is attached. The first diaphragm section 5 and the second diaphragm section 6 are made of a base material that is impregnated in a thermosetting resin, and the attachment 7 is formed by hardening the thermosetting resin. This loudspeaker diaphragm reduces a loss in transmission of driving force from the voice coil bobbin, and accordingly, a loudspeaker employing this loudspeaker diaphragm can improve the S/N ratio.
Moreover, as another effort, a loudspeaker has been provided in which a cone diaphragm and a bobbin of a voice coil are both coupled to a dome diaphragm. Typically, for example, such a loudspeaker is allowed to expand high-pass limiting frequencies, and to extend and connect the bobbin of the voice coil to a portion in the vicinity of a joint of vibration of the dome diaphragm so as to obtain a smooth sound pressure response over broad band frequencies, and to connect an outer circumference of the dome diaphragm to a portion in the vicinity of a joint of vibration of the cone diaphragm (Japanese Laid-Open Patent Publication No. S62-150997).
Furthermore, an inverted dome loudspeaker, whose shape of the diaphragm in a front vertical cross-sectional view is such that a curved surface is protruded downwardly in a dome shape, has been provided, in which a diaphragm 1 is formed by injection molding with a thermoplastic resin as a main material, a rib group 15 including a plurality of ribs 15a, 15b, 15c, 15d, and . . . provided in a concentric pattern is disposed on a back side of the diaphragm 1, a voice coil bobbin 2 is fixedly attached to the diaphragm 1 using one of the ribs of the rib group 15 as a guide, and a ring-shaped throat 22 is provided between the voice coil bobbin 2 and a different rib of the rib group 15 (Japanese Laid-Open Patent Publication No. H09-247791).
However, in a loudspeaker having the structure as shown in FIG. 3 of Japanese Laid-Open Patent Publication No. H09-247791, as described in paragraph 0021 of the specification, “in some cases, in order to adjust desired characteristics, the diaphragm land the voice coil bobbin 2 are connected only by adhesion between the diaphragm 1 and the throat 22, and the voice coil bobbin 2 and the diaphragm 1 are not directly attached”. As can be seen from the description “workability is improved” in the same paragraph, this is due to the fact that it is extremely difficult, for a loudspeaker designed such that a cone diaphragm and a bobbin of a voice coil are both coupled to a dome diaphragm, to produce stable loudspeakers in which an end of the outer circumference of the cone diaphragm is closely coupled to the dome diaphragm, and the bobbin of the voice coil is closely coupled to the dome diaphragm because the production is affected by dimensional tolerance and assembly tolerance of components for the dome diaphragm, the cone diaphragm, and the bobbin of the voice coil. Specifically, in the production of a loudspeaker having a dome diaphragm and a cone diaphragm, due to variations in the tolerance for components, there can be such problems in which a back side of the dome diaphragm and the bobbin of the voice coil are spaced apart, the end of the outer circumference of the dome diaphragm and the end of the outer circumference of the cone diaphragm are spaced apart, and either the dome diaphragm or the cone diaphragm is deformed and the diaphragms are coupled with a stress being applied therebetween. This disadvantageously hinders stable production of loudspeakers, resulting in deterioration of playback sound quality.
The present invention is contrived in order to address the problems found in the conventional techniques listed above, relating to loudspeakers in which a cone diaphragm and a bobbin of a voice coil are both coupled to a dome diaphragm. An object of the present invention is to provide a loudspeaker that can be stably produced, in which adhesive strength between the dome diaphragm, the cone diaphragm, and the bobbin of the voice coil that constitute a vibration system is high, and whose playback sound quality is excellent with a small peak dip in sound pressure frequency characteristics.